Ectopleura larynx is a colonial hydroid that produces dense clusters of pink-tipped polyps on upright stalks, each 10–40 mm tall. The colonies form bushy tufts attached to substrates by a creeping stolon network. This species is among the fastest-colonising macrofoulers in cold-temperate waters, appearing on freshly deployed nets in Norwegian and Scottish salmon farms within 7–14 days of immersion. It ranges across the North Atlantic from arctic Norway to the English Channel.
Hydroid fouling matters for two reasons. First, dense Ectopleura coverage — sometimes reaching 100 % of the net surface within a month — reduces water exchange through the mesh by 30–60 %, lowering oxygen delivery to caged fish. Second, hydroid colonies trap fine sediment and organic particles, creating a substrate that mussels, barnacles, and other heavier foulers settle on. In effect, Ectopleura accelerates the entire fouling succession. Farms in high-fouling fjords report cleaning costs rising by 15–25 % when hydroids dominate — run your own numbers with the cost calculator.
In-situ net cleaning with rotating disc machines removes hydroid growth effectively, but colonies regrow within weeks during the summer fouling season. Copper-alloy nets and copper-based coatings suppress settlement substantially. Farms using cleaner fish (wrasse) report partial grazing on young hydroid colonies, though the effect varies. For a detailed look at anti-fouling options, see the methods comparison. The related Obelia hydroid presents a similar but lighter fouling challenge.
Control Methods
In-situ net cleaning Anti-fouling coatings Net changes Copper-alloy nets